Evolutionary convergence in amphibians between Australia and southern Africa depends on predatory regimes rather than just climates and soils

@alexanderr @spixii @stephenmahony @reiner @mothchild @briancadam @patrick_campbell @tom-kirschey @joelknightnz @adammyates @asimakis_patitsas @olvr_a @calebcam @tyroneping @herping_with_berks @rion_c @danieleseglie @smuele @johngsalamander @franciscodocampo @martin_schluepmann @tszentiv @samuel_guiraudou @stamatiskalogiannis @grathwohl @amarzee @ilias_strachinis @ludwig_muller @sandboa

I have shown, in other Posts, that there is negligible evolutionary convergence (https://en.wikipedia.org/wiki/Convergent_evolution) between Australia and southern Africa, in

Having covered the above groups, I now turn to amphibians.

To make intercontinental comparison as rigorous as possible, I have chosen study areas carefully matched in climates, landforms and soils: Fitzgerald River National Park (https://en.wikipedia.org/wiki/Fitzgerald_River_National_Park) and its environs in Western Australia and Agulhas National Park (https://en.wikipedia.org/wiki/Agulhas_National_Park) and its environs in South Africa.

The results:

All the amphibians in the study areas are anurans.

In sharp contrast to vertebrate-eating birds, the faunas of amphibians in the study areas are so phylogenetically different that not even a single family is shared intercontinentally.

This means that any close similarity in the forms and functions of the anurans between the continents is likely to result from evolutionary convergence rather than ancestral recruitment of similar forms. Unrelated intercontinental counterparts have presumably been modified by natural selection to conform in their adaptations to similar environments.

However, the similarities to be found in these local faunas are minor. Once again it is the differences that seem important.

As in the mammals, snakes, and vertebrate-eating birds, the anurans are more differentiated in the southern African study area than in the Australian study area. This includes differentiation in body sizes.

Absent from the Australian study area are any counterparts to the following:

Absent from the southern African area are any counterparts to the following:

The anurans in the Australian study area are weakly defended against predation, even relative to their congeners in eastern Australia. For example, only one species in or near Fitzgerald River National Park is known to inflate its body when accosted, whereas this tactic is obvious in several genera in the southern African study area.

Perhaps the closest counterparts in the two study areas, showing considerable evolutionary convergence, are the limnodynastid Neobatrachus albipes (https://www.inaturalist.org/observations/26018363) in Australia and the pyxicephalid Tomopterna delalandii (https://www.inaturalist.org/observations/38250345 and https://thebdi.org/2022/02/21/cape-sand-frog-tomopterna-delalandii/ and http://frogmap.adu.org.za/Species_text.php?sp=1000) in South Africa. Both are small but stout frogs that breed in seasonal pools and shelter underground during the dry summer.

However, a certain pattern is far more noticeable in amphibians than in mammals, snakes or vertebrate-eating birds.

This is that potential counterparts do in some cases occur somewhere on these landmasses, but without precise correspondence in the physical environment (latitude, climate, and soil).

The clearest examples of this 'geographical displacement' in evolutionary convergence can be found in the remarkably speciose and heterogeneous pelodryadid genera Litoria (https://en.wikipedia.org/wiki/Litoria) and Ranoidea (https://en.wikipedia.org/wiki/Ranoidea_(genus)).

These examples are as follows:

The remarkable 'plasticity' in form and function of pelodryadids - which to this day continue to defy traditional taxonomy - indicates that any failure of adaptive matching in the study areas is hardly owing to phylogenetic constraints.

So, this is the important finding:

Lookalikes for several of the species in and near Agulhas National Park can be found, but not in or near Fitzgerald River National Park - or for that matter anywhere in the southwestern third of Australia. Instead they occur on the other side of Australia, under different climates.

This indicates that the failure of adaptive matching in the study areas is owing to subtle differences in the biotic environment (particularly the intensity of the predatory regime), rather than to any small differences remaining in the physical environment.

This seems to make sense in terms is the biogeography of islands.

The full suite of selective pressures associated with continents does not reach the southwestern tip of Australia. This is the most isolated part of an island continent because it is separated from eastern and northern Australia by semi-arid tracts, barring most predators. By contrast the full intensity of the African predatory regime extends uninterrupted all the way to the southwestern tip of South Africa.

The result is what seems to be a pattern of geographic displacement in evolutionary convergence.

For amphibians, the Australian study area - despite its close similarity in climate and soils to the southwestern tip of southern Africa - is effectively on an island as much as on a continent. This isolation is reflected in the nature of its anuran fauna, which has been shaped as much by its relative freedom from predation as by its latitude, climate, and soils.

A similar explanation applies, less cleary, to certain snakes I have discussed in previous Posts (see https://www.inaturalist.org/journal/milewski/62557-no-evolutionary-convergence-between-australia-and-southern-africa-in-snakes-and-legless-lizards-part-2#).

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FITZGERALD RIVER NATIONAL PARK and environs, WESTERN AUSTRALIA

Limnodynastidae:

Heleioporus albopunctatus https://www.inaturalist.org/taxa/22045-Heleioporus-albopunctatus and https://museum.wa.gov.au/explore/frogwatch/frogs/western-spotted-frog

Heleioporus eyrei female SV up to 6.3 cm https://www.inaturalist.org/taxa/22046-Heleioporus-eyrei

Heleioporus psammophilus https://www.inaturalist.org/taxa/22044-Heleioporus-psammophilus

Limnodynastes dorsalis female SV up to 8.7 cm https://www.inaturalist.org/taxa/22035-Limnodynastes-dorsalis

Neobatrachus albipes SV up to 4.5 cm https://www.inaturalist.org/taxa/22074-Neobatrachus-albipes

Neobatrachus pelobatoides female SV up to 4.5 cm https://www.inaturalist.org/taxa/22077-Neobatrachus-pelobatoides

Myobatrachidae:

Crinia georgiana female SV 3-3.6 cm https://www.inaturalist.org/taxa/25232-Crinia-georgiana

Crinia pseudinsignifera https://www.inaturalist.org/taxa/25236-Crinia-pseudinsignifera

Crinia subinsignifera https://www.inaturalist.org/taxa/25235-Crinia-subinsignifera

Metacrinia nichollsi https://www.inaturalist.org/taxa/25304-Metacrinia-nichollsi and see https://www.researchgate.net/publication/315304182_Evolutionary_and_natural_history_of_the_turtle_frog_Myobatrachus_gouldii_a_bizarre_myobatrachid_frog_in_the_southwestern_Australian_biodiversity_hotspot

Myobatrachus gouldii up to 5 cm https://www.researchgate.net/publication/315304182_Evolutionary_and_natural_history_of_the_turtle_frog_Myobatrachus_gouldii_a_bizarre_myobatrachid_frog_in_the_southwestern_Australian_biodiversity_hotspot and https://www.inaturalist.org/taxa/25298-Myobatrachus-gouldii

Pseudophryne guentheri 3 cm https://www.inaturalist.org/taxa/25254-Pseudophryne-guentheri

Pelodryadidae:

Litoria adelaidensis up to 4.7 cm https://www.inaturalist.org/taxa/23618-Litoria-adelaidensis

Ranoidea cyclorhynchus 5.5-7.5 cm https://www.inaturalist.org/taxa/517081-Ranoidea-cyclorhynchus

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AGULHAS NATIONAL PARK and environs, SOUTH AFRICA

Brevicepitidae:

Breviceps acutirostris marginal to study area on northwestern side https://www.inaturalist.org/taxa/25000-Breviceps-acutirostris

Breviceps montanus SV 3.8? cm https://www.inaturalist.org/taxa/24994-Breviceps-montanus

Breviceps rosei vansoni SV 2.6 cm https://www.inaturalist.org/taxa/24992-Breviceps-rosei

Bufonidae:

Sclerophrys capensis SV up to 12 cm https://www.inaturalist.org/taxa/517132-Sclerophrys-capensis

Sclerophrys pantherina female SV 12.2 cm https://www.inaturalist.org/taxa/517449-Sclerophrys-pantherina and https://zslpublications.onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1992.tb04431.x and https://neag.org.za/wp-content/uploads/10.2305_IUCN.UK_.2016-3.RLTS_.T54723A77159333.en_.pdf

Vandijkophrynus angusticeps SV 6.8 cm https://www.inaturalist.org/taxa/67258-Vandijkophrynus-angusticeps and https://www.tyroneping.co.za/amphibians-of-southern-africa/vandijkophrynus-angusticeps-cape-sand-toad/

Hyperoliidae:

Hyerolius horstockii SV 3.5 cm up to 4 cm https://www.inaturalist.org/taxa/23370-Hyperolius-horstockii

(Hyperolius marmoratus https://www.inaturalist.org/taxa/23331-Hyperolius-marmoratus)

Semnodactylus wealii https://www.inaturalist.org/taxa/23528-Semnodactylus-wealii

Pipidae:

Xenopus gilli https://www.inaturalist.org/taxa/25453-Xenopus-gilli

Xenopus laevis https://www.inaturalist.org/taxa/25457-Xenopus-laevis

Pyxicephalidae:

Amietia fuscigula SV 9.5 cm https://www.inaturalist.org/taxa/64912-Amietia-fuscigula

Arthroleptella villiersi SV 2.2 cm https://www.inaturalist.org/taxa/25325-Arthroleptella-villiersi

Cacosternum australis SV 1.9? cm https://www.inaturalist.org/taxa/476925-Cacosternum-australis

Microbatrachella capensis SV 1.5-1.8 cm and up to 2.0 cm https://www.inaturalist.org/taxa/25432-Microbatrachella-capensis and https://amphibiaweb.org/species/3734

Strongylopus bonaespei https://www.inaturalist.org/taxa/26212-Strongylopus-bonaespei

Strongylopus fasciatus SV 4.7 cm marginal to study area on eastern side https://www.inaturalist.org/taxa/26218-Strongylopus-fasciatus

Strongylopus grayii SV 4.2 cm https://www.inaturalist.org/taxa/26214-Strongylopus-grayii

Tomopterna delalandii SV 4.8 cm https://www.inaturalist.org/taxa/25806-Tomopterna-delalandii

Publicado el marzo 7, 2022 12:11 TARDE por milewski milewski

Comentarios

@alexanderr Hi Alex, Have you ever seen self-defensive inflation in any species of Tomopterna? With thanks from Antoni.

Publicado por milewski hace casi 2 años

The tropical species Notaden melanoscaphus (https://www.inaturalist.org/observations/86411292) achieves superficial similarity to Breviceps montanus (https://www.inaturalist.org/observations/11044936). However, the reproductive modes remain categorically different.

Publicado por milewski hace casi 2 años

Not personally, but there are photos showing them doing it:
https://www.facebook.com/photo/?fbid=4081019838595879&set=pcb.3625728694129624
https://www.facebook.com/photo/?fbid=567853323786395&set=pcb.2486467181389120
https://www.facebook.com/photo/?fbid=326269958197500&set=pcb.1919791358056708

It seems to be a general frog defense mechanism against snakes, and I think most would try it if attacked.

I'm sure there are some interesting strategies by snakes, like popping the lungs of frogs with their fangs or slitting open the belly so that the lungs expand outside of the body. Check this recent Philothamnus observation: https://www.inaturalist.org/photos/182348028

Publicado por alexanderr hace casi 2 años

Just as the mammalian fauna consists particularly of marsupials in Australia, this theme of faunal predominance and adaptive radiation occurs also in anuran amphibians and snakes. In the case of anuran amphibians, a remarkable radiation has occurred in Pelodryadidae, taking a range of forms and functions that would be taken by several families on any other continent. In the case of snakes, "There are more than 130 described species of Australian elapids. They are the largest and most diverse group of snakes in Australia".

Publicado por milewski hace casi 2 años

The smallest-bodied species of anuran in Australia, namely Microhylidae: Cophixalus exiguus (https://en.wikipedia.org/wiki/Scanty_frog), is about the same size (1.6-1.9 cm) as the smallest-bodied species of anuran in southern Africa, namely Pyxicephalidae: Microbatrachella capensis (https://en.wikipedia.org/wiki/Micro_frog), 1.8 cm. However, the former occurs only in the tropics (in rainforest) whereas the latter occurs at the southern tip of Africa (in seasonal marshes).

Publicado por milewski hace casi 2 años

Cacosternum australus might be the ecological counterpart to Crinia georgiana?

Publicado por alexanderr hace casi 2 años

@alexanderr

Hi Alex, I do not see Crinia georgiana and Cacosternum australis as intercontinental counterparts.

Crinia georgiana is a rather generalised frog except for its fairly small body size and rather large eggs. It is part of a pattern of limited differentiation in the anuran fauna under the winter-rainfall climate in Australia.

The anuran fauna under the winter-rainfall climate in South Africa is remarkably differentiated, including in body size. The species range from 'micro frogs' to toads weighing perhaps more than 400 grams.

The only information I have seen on the body size of C. australis is that in Channing et al. (2013): one adult male individual of body length 17.7 cm. This is considerably smaller-bodied than C. georgiana. Female body length in the Australian species is 3-3.6 cm, whereas I suspect that female body length in C. australis is always less than 2.5 cm, giving it about half the body mass of C. georgiana.

In the southern African study area there is a diminutive trend involving Microbatrachella, Arthroleptella, and Cacosternum, all of which have body lengths less than 2.5 cm. This is not mirrored in the Australian study area.

Furthermore, Crinia georgiana does not seem to bury itself during the dry summer, whereas I assume that the C. australis does. The situation is confusing because Crinia glauerti, which falls just short of the Australian study area on the western side, is stated to bury itself in the dry season.

I get the impression that the eggs and larvae of C. georgiana are adapted to nutrient-poor water such that the newly-metamorphosed juveniles are far smaller than the adults. By comparison in Microbatrachella capensis the newly-metamorphosed juveniles approach adults in body size. I suspect that Cacosternum australis resembles M. capensis in this way.

So I suggest that in and near the southern African study area there is a faunal component of relatively diminutive pyxicephalid frogs with no counterparts in Australia. These range from A. villiersi on acidic slopes through M. capensis on acidic flats to C. australis on neutral to alkaline flats.

Your further thoughts?

Publicado por milewski hace casi 2 años

@alexanderr Southwestern Western Australia does have anurans about as small-bodied as the micro-frogs of the southwestern Cape of South Africa.

These are four species of Geocrinia (https://en.wikipedia.org/wiki/Geocrinia) in the family Myobatrachidae: Geocrinia alba (https://www.inaturalist.org/taxa/25242-Geocrinia-alba), G. lutea (https://www.inaturalist.org/taxa/25244-Geocrinia-lutea), G. rosea (https://en.wikipedia.org/wiki/Geocrinia_rosea) and G. vitellina (https://en.wikipedia.org/wiki/Geocrinia_vitellina). All have SV length 25 mm or less when fully-grown.

The difference is that these species of Geocrinia live in forest, not the low vegetation inhabited by Arthroleptella, Cacosternum, and Microbatrachella in South Africa. Furthermore, in Geocrinia the larval stage is completed out of water, not by means of swimming tadpoles.

So the small body size is about the only real similarity intercontinentally, and Geocrinia cannot be considered evolutionarily convergent with the South African 'micro-frogs' overall.

Publicado por milewski hace casi 2 años

The larvae of some of the species in the southern African study area have been described as follows by D E van Dijk (1972), Zoologica Africana 7 (1): 49-55.

Xenopus larvae pelagic, filter-foraging, suspended in water in head-down position

Cacosternum and Microbatrachella larvae pelagic/hydrophytophilic

Hyperolius larvae pelagic/hydrophytophilic but tending to perch on submerged plants

Strongylopus fasciatus larvae hydrophytophilic with pelagic habit

Strongylopus grayi larvae bottom-dwelling hydrophytophilic

Tomopterna larvae bottom-dwelling

Amietia larvae bottom-dwelling, in back-waters of streams

Sclerophrys larvae bottom-dwelling

Breviceps larvae subterranean

Arthroleptella larvae extra-aquatic on moss

Publicado por milewski hace casi 2 años

Ah ok, it was just a guess because they were small and seem to breed in temporary water bodies, like Cacos.

"The anuran fauna under the winter-rainfall climate in South Africa is remarkably differentiated, including in body size. The species range from 'micro frogs' to toads weighing perhaps more than 400 grams." Many montane species tend to be smaller, but Cacosternum specifically are very common and widespread in South Africa, Namibia and Zimbabwe (see boettgeri) and maintain these small body sizes throughout their range.

"I get the impression that the eggs and larvae of C. georgiana are adapted to nutrient-poor water such that the newly-metamorphosed juveniles are far smaller than the adults. By comparison in Microbatrachella capensis the newly-metamorphosed juveniles approach adults in body size. I suspect that Cacosternum australis resembles M. capensis in this way." They are smaller than adults, but perhaps not to the degree you are talking about with C. georgiana.

"So I suggest that in and near the southern African study area there is a faunal component of diminutive pyxicephalid frogs with no real counterparts in Australia. These range from A. villiersi on acidic slopes through M. capensis on acidic flats to C. australis on neutral to alkaline flats."
Interesting, any reason why there are no small frogs in Australia? We get small Cacos even in arid regions.

Publicado por alexanderr hace casi 2 años

According to https://www.researchgate.net/publication/316882457_Length_-_Mass_allometries_in_Amphibians, an anuran of SV length 15 millimeters is predicted to weigh 0.2 grams.

Publicado por milewski hace casi 2 años

'Pseudo-toadlets' in the bufonid genus Capensibufo (https://www.inaturalist.org/observations?place_id=any&taxon_id=21817&view=species) would provide a fair counterpart to the myobatrachid Pseudophryne guentheri (https://www.inaturalist.org/taxa/25254-Pseudophryne-guentheri) found in the Australian study area. However, none of the four species of Capensibufo reach the southern African study area.

Publicado por milewski hace casi 2 años

Termites in the diet of Myobatrachus gouldii:

Vertucci et al. (2017) https://www.researchgate.net/publication/315304182_Evolutionary_and_natural_history_of_the_turtle_frog_Myobatrachus_gouldii_a_bizarre_myobatrachid_frog_in_the_southwestern_Australian_biodiversity_hotspot

Calaby 1956: 100% (in stomachs of specimens collected inside a termitarium)

Mike Bamford (1986): 93.5% in stomachs of specimens captured near Gingin (https://researchrepository.murdoch.edu.au/id/eprint/41575/)

Peter Murray (1980, BSc Hons thesis, Murdoch University) 24% of prey items in stomachs of specimens pitfall-trapped in Badgingarra National Park

Publicado por milewski hace casi 2 años

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